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Old 09-01-2010, 04:54 PM   #1
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Various A/C questions - return vents, leaking air in unit, hot upstairs...


So I'm living in a 2 story house with a basement built in 2001. The house has 2 AC units one for upstairs, then other for downstairs and basement. This is a rather large house and the cooling/heating bills are more than what we'd wish for. The top of the house is the hottest (not by much) as one would expect the hot air goes up, cold goes down. Basement is very cold. There is a foyer? or a 2 story room when you enter the main door - an open area from 1st floor to 2nd floor and a small balcony/railing overlooking it on the 2nd floor.

So here are the questions I have about the situation:

The question of return vents.

I see that on both floors are top and bottom vents and the bottom ones can be closed. Both top and bottom return vents have always been open but from what i think, in the summer, the bottom should be closed so the hot air from the TOP gets drawn in, correct? Also, when i close the bottom ones, i hear humming which i'm assuming to be just air flow through tight airspace when the wings are closed. My concern however is if that may cause any problems with overloading/pressure in the unit if not properly balanced. Which brings me to the next question:

Balancing air flow?

The basement has all the outbound vents closed as its already very cool. The door to the basement has air being forced DOWNSTAIRS through the gap below the door. There's a significant amount of (cold) air being forced downstairs. Should i correct this somehow? How does one properly balance input/output of the air flow in a home central AC system? (2 ac's). Would it help to seal that door or would that cause trouble to the units? I'm not sure that when the house was built the contractors did everything well (given other problems). I'd like to re-asses the whole situation of the heating/cooling.

Leaking units

So the basement is very chilly and i'd like to think of a way to get that cold air up. The main problem i see is that the units in the basement leak cold air. What i'm referring to as the unit is in the basement, big furnace/pump? that seems to blow it all throughout the house (there are 2 of them). There are small areas around the entire unit where cold air just swooshes out. I see there are parts that are duck-taped or silver-taped. Can i safely duck-tape leaking holes/areas? I don't want to start duck-taping randomly as I'm worried I'd cover something important that i shouldn't. Can you advise me as to what's safe and what's not? I'm also inspecting some of the duct work and i see/feel many areas where air is also leaking. I guess just duck tape the heck out of it?

Any other advice you can give me to increase the efficiency would be very welcome. Also, i'm testing whether running the fan only takes care of bringing up the cold air from the basement - any thoughts?

I'd very much appreciate:

  • Input from professionals
  • Ways i can quantify air flow issues
  • Simple tests i can perform to see if what i'm doing is making a difference (i'm going to test total run time hours on the thermostats of AC's after making changes)
  • Pointing me to sources and resources where i can learn/look things up without taking an HVAC course. (books, websites, community programs).
Thank you for your input (and output)
PolishPaul

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Old 09-02-2010, 01:04 AM   #2
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Various A/C questions - return vents, leaking air in unit, hot upstairs...


After some observation i'm concerned about the air returning to the basement via the door. There's quite a lot of air coming back, the door will get pulled shut when the AC is running. Should that pressure be neutral or slightly negative?

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Old 09-02-2010, 09:34 AM   #3
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Various A/C questions - return vents, leaking air in unit, hot upstairs...


don't use duct tape. you can buy the silver (aluminum) tape at any big box store like lowe's or home depot. don't get just any aluminum foil, get the wider, more expensive stuff designed for ductwork. you can also use duct sealant or mastic that is kind of like a thick past that you paint on and it stays pliable when it dries.
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Old 09-02-2010, 09:56 AM   #4
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Various A/C questions - return vents, leaking air in unit, hot upstairs...


Quote:
Originally Posted by PolishPaul View Post
the bottom should be closed so the hot air from the TOP gets drawn in, correct?

How does one properly balance input/output of the air flow in a home central AC system? (2 ac's).

Can i safely duck-tape leaking holes/areas? I don't want to start duck-taping randomly as I'm worried I'd cover something important that i shouldn't. Can you advise me as to what's safe and what's not?
Leave all returns open. That's probably the reason the basement door is being sucked open.

Balance is achieved using volume dampers in duct branches.

As PoplishPaul said, cloth duct tape shouldn't be used to seal duct. (I wish they never would have named it "duct tape"). Use mastic (we use ProSeal in gallon tubs and apply it with a paint brush) or aluminum "foil" tape.
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Old 09-02-2010, 01:05 PM   #5
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Various A/C questions - return vents, leaking air in unit, hot upstairs...


I tested by opening all return ducts and closing the ones i could and i see no difference at all. I also closed/opened basement doors which lead to the units and also no difference.

I don't see any handles that i'd expect to see in a volume dampener - aren't they for controlling the air coming out of the AC and into the room?
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